The present invention relates to a solid electrolytic capacitor used in a variety of electronic equipment and a manufacturing method thereof.
FIG. 30 is a perspective view showing the structure of a prior art solid electrolytic capacitor and FIG. 31 is a perspective view showing the structure of a solid electrolytic capacitor element stack unit. In FIG. 30 and FIG. 31, capacitor element 50 is an anode body composed of aluminum foil, the aluminum being a valve action metal, and divided into anode member 50A and cathode member 50B. Further, cathode member 50B has a dielectric oxide film layer, solid electrolyte layer and cathode layer (none of these are shown in the drawings) stacked on top of each other in layers on the surface thereof in succession.
Capacitor element stack unit 51 is constructed as described below:
1A) A conductive silver paste (not shown in drawings) is applied onto cathode unit terminal 52 to join with cathode member 50B.
2A) Cathode member 50B of another capacitor element is joined with cathode member 50B by applying a conductive silver paste (not shown in the drawings) thereto.
3A) By repeating the steps 1) and 2) by a plurality of times, a plurality of capacitor elements 50 are stacked on top of each other in layers.
4A) Then, respective anode members 50A of the plurality of capacitor elements 50 are integrally connected with anode unit terminal 53.
By using capacitor element stack unit 51 thus prepared, a solid electrolytic capacitor is constructed as follows:
5A) Cathode member 50B of capacitor element stack unit 51 is joined onto cathode lead frame 54 via a conductive silver paste (not shown in the drawings).
6A) Another capacitor element stack unit 51 is stacked on cathode member 50B via a conductive silver paste (not shown in the drawings).
7A) By repeating the steps 5) and 6) by a plurality of times, a plurality of capacitor element stack units 51 are stacked on top of each other in piles.
8A) Respective anode members 50A of the plurality of capacitor element stack units 51 are integrally connected with anode lead frame 55.
9A) The plurality of capacitor element stack units 51 are encapsulated with an insulating packaging resin (not shown in the drawings) in such a way as part of respective anode lead frame 55 and cathode lead frame 54 is exposed on the outer surfaces of the insulating packaging resin.
FIG. 32 is a cross-sectional view of another prior art solid electrolytic capacitor structured differently from the one shown in FIG. 30. FIG. 33 is a perspective view of a capacitor element used in the solid electrolytic capacitor of FIG. 32, and FIG. 34 is a perspective view showing how a plurality of the capacitor elements are stacked on top of each other in layers on anode/cathode lead frames.
In FIG. 32 to FIG. 34, capacitor element 56 is an anode body formed of aluminum foil (not shown in the drawings), the aluminum being a valve action metal, and divided into anode member 59 and cathode member 60 by providing resist part 58 after a dielectric oxide film layer (not shown in the drawings) is formed on the surface of the anode body. Further, a solid electrolyte layer and cathode layer (none of these are shown in the drawings) are stacked on top of each other in layers on the surface of cathode member 60 in succession.
A capacitor element stack body of FIG. 34 is constructed as described below:
1B) A plurality of capacitor elements 56 are stacked on top of each other in layers in such a way as having anode member 59 disposed on both upper and bottom surfaces of anode lead frame 61 and also having cathode member 60 disposed on both upper and bottom surfaces of cathode lead frame 62.
2B) Respective anode members 59 are joined integrally with anode lead frame 61 by resistance welding.
3B) Respective cathode members 60 are connected integrally to connecting member 62A provided on cathode lead frame 62 on the side surfaces of capacitor element 56 extending in the thickness direction thereof via a conductive silver paste (not shown in the drawings).
Additionally, connecting member 62A is armed by bending part of a flat member of cathode lead frame 62 into a right angle.
By using the capacitor element stack body of FIG. 34 thus prepared, the solid electrolytic capacitor of FIG. 32 is constructed as follows:
1C) The capacitor element stack body is encapsulated with an insulating packaging resin 63 in such a way as part of respective anode lead frame 61 and cathode lead frame 62 is exposed on the outer surfaces of packaging resin 63.
2C) Anode lead frame 61 and cathode lead frame 62 exposed from packaging resin 63 are respectively bent along the surface of packaging resin 63. (This is not shown in the drawings.)
The solid electrolytic capacitor shown in FIG. 30 is prepared by first producing capacitor element stack unit 51 by stacking a plurality of capacitor elements 50 on top of each other in layers and then by further stacking a plurality of capacitor element stack units 51 on top of each other in piles. Accordingly, not only a great variety of component parts are used but also the assembly work becomes complex, thereby ending up with a high cost product.
As described in above, by applying a conductive silver paste onto respective stack surfaces of a plurality of capacitor elements 50, capacitor elements 50 are connected with one another electrically to construct capacitor element stack unit 51. Furthermore, a plurality of capacitor element stack units 51 are stacked on top of each other in piles with a conductive silver paste applied therebetween to connect electrically between capacitor element stack units 51. Finally, part of cathode lead frame 54 located on the bottom of the stack of capacitor element stack units 51 forms a cathode terminal for external connection, thereby making it difficult for equivalent series resistance (referred to as ESR on occasions, hereafter) characteristics to be made closer to theoretical ones since the distance of cathode lead tends to be long.
The ESR characteristics of the setup as described in above are demonstrated by a summation of the following resistance values as shown in a schematic illustration of FIG. 35:
A) Resistance R1 produced between the layers of capacitor element 50 that constitute capacitor element stack unit 51.
B) Resistance R2 produced between the piles of capacitor element stack unit 51.
Therefore, as the number of layers of capacitor element 50 and the number of piles of capacitor element stack unit 51 increase, an alienation between actual ESR characteristics and theoretical ones is growing.
Additionally, since there exists a conductive silver paste between respective neighboring capacitor elements 50 and also between respective neighboring capacitor element stack units 51, the dimensions in the height direction thereof become large, thereby making it difficult for the end product of solid electrolytic capacitor to be reduced in thickness.
With the solid electrolytic capacitor of FIG. 32, a plurality of anode members 59, each provided to capacitor element 56, are integrally joined to anode lead frame 61 by resistance welding as described in above. However, as FIG. 36 shows, dielectric oxide film layer 56B is formed on the surface of aluminum foil 56A in anode member 59. When anode member 59 is joined to copper made anode lead frame 61 by resistance welding, dielectric oxide film layer 56B having a high value in resistance makes it hard for the welding currents to flow. As a result, only part of aluminum foil 56A is welded onto anode lead frame 61 or aluminum foil 56A is not welded onto anode lead frame 61 at all in the bad case. Therefore, not only defective capacitors due to insufficient welding strength are produced but also an increase or a wide range of variation in equivalent series resistance may be caused.
In order to solve the foregoing problems, an increase of welding currents or the adoption of laser welding is well worth considering. However, such countermeasures as above may cause new problems as follows:
Molten aluminum foil 56A may extend to such places as cut sections of anode member 59 and the like, where aluminum foil 56A is exposed, or may be splashed to impair an outward appearance. The thickness of packaging resin 63 is reduced by a comparable amount of molten aluminum foil 56A, thereby causing such problems as a reduction in hermeticity. A short circuit occurs, and the like.
On the other hand, since the thickness of anode member 59 is less than the thickness of cathode member 60, a gap is created between neighboring anode members 59 when capacitor elements 56 are stacked on top of each other in layers. When respective anode members 59 are integrally joined onto anode lead frame 61 by resistance welding, a pressing force is applied via welding electrode 64 to crush the aforementioned gap. At this time, anode member 59 is bent and the extent of bending of anode member 59 is more pronounced as the distance of anode member 59 from anode lead frame 61 increases. Therefore, an excessive deformation of anode member 59 due to the bending results in cracks created in part of dielectric oxide film layer 56B or sometimes in a breakage thereof, thus causing a leakage current (LC) failure.
With a solid electrolytic capacitor of the present invention, an anode lead frame is connected to anode members of a capacitor element stack body which is formed by stacking a plurality of capacitor elements on top of each other in layers while a cathode lead frame has a connecting member to connect integrally with cathode members of the capacitor element stack body on the side surface thereof extending in the thickness direction of the capacitor element, thereby allowing a reduction in component count and enhancement of productivity in assembly work to be realized with a simplified structure. Moreover, since a cathode is taken from the side surface of the cathode member of the capacitor element, the distance of a cathode lead is shortened, resulting in a remarkable improvement in equivalent series resistance characteristics. Furthermore, no conductive silver paste is disposed between neighboring stack layers, thereby allowing the thickness of the capacitor to be reduced.
Further, with the solid electrolytic capacitor of the present invention, capacitor elements, each anode member of which has a through hole, are stacked on top of each other in layers and an anode lead frame is connected with stacked capacitor elements. Accordingly, when a plurality of anode members are joined onto the anode lead frame via the through hole provided on the anode member of each respective capacitor element, a stabilized welding work is allowed to be conducted without such problems as splashing of molten aluminum foil and the like. Also, an excellent joining strength, enhanced reliability and a remarkable improvement in equivalent series resistance are achieved.